This invention relates to telephone line circuits and particularly to a battery feed circuit for a telephone line having a plurality of stations.
In a telephone subscriber loop arrangement comprising a plurality of telephone stations, d.c. voltage for powering transmitter microphones and for various signaling generally is often supplied locally. There is a need, in all types of telephone circuits, to reduce noise signals induced in the telephone line, characteristically common mode signals, without degrading differential mode talking signals. Interference both from local crosstalk and the power supply are likely. Prior circuits utilized inductors to provide suitable power supply isolation and more recently electronic circuits have been disclosed for both common and local battery feed to telephone lines which avoid the inclusion of inductors. However, there is a continuing need for local battery feed arrangements which provide greater common mode interference reduction as well as elimination of locally produced noise. Moreover, it is desirable to implement a telephone line local battery feed circuit using solid state integrated circuit technology to the greatest possible extent.